Abstract On the basis of molecular orbital calculations we study several three dimensional arrangements of ligands with respect to iron in iron-pentacyanide complexes, in FeOCl, and in deoxygenated heme compounds. For the various molecular structures under study we derive electric field gradient (EFG) tensors, from which we calculate quadrupole splittings, asymmetry parameter, and orientations of the EFG component Vzz, which are compared with experimental data.